Device for stacking sheets for printing machine

ABSTRACT

A device for stacking sheets for a printing machine, including at least a sheet deflection device which can be driven in rotation, and which is provided for receiving or grabbing a front edge of a sheet and for stacking the sheet after it has moved through a rotation path, and having at least two sheet conveyance devices that can be rotated substantially independently of each other about the common axle, and thus one of these sheet conveyance devices is ready to receive or grab a next sheet, when another one of these sheet conveyance devices is still occupied with the transport and the stacking of a preceding sheet.

FIELD OF THE INVENTION

The invention relates to a device for stacking sheets for a printingmachine, preferably an electrophotographic printing machine, comprisingat least a drivable sheet conveyance device which can be driven inrotation, and which is provided for receiving or grabbing a front edgeof a sheet and for stacking the sheet after it has moved through arotation path.

BACKGROUND OF THE INVENTION

A stacking device for sheets, which includes a sheet conveyance device,which can be driven in rotation, is known, for example, from U.S. Pat.No. 4,252,309. In this known stacking device, the front edge is insertedinto a slit of the substantially disk-shaped sheet conveyance device.The sheet, which has thus been grabbed, is moved along by an uppergrabbing place by a half rotation of the sheet conveyance device andturned, and then it is stacked on the reached lower level on a stackingplace where it is stacked on other sheets. The sheet to be stacked isreleased automatically from the sheet because the conveyance devicemoves past a stop, which retains the sheet.

SUMMARY OF THE INVENTION

The invention is based on the problem of providing a variant of a sheetstacking device, which is such that the device can be used optimally,and it is preferably also suitable for sheets having different formatsand weights.

This problem is solved according to the invention by the fact that atleast two sheet conveyance devices are provided, in such a manner thatthese several sheet conveyance devices can be rotated substantiallyindependently of each other about the common axle, and thus one of thesesheet conveyance devices is ready to receive or grab a next sheet, whenanother one of these sheet conveyance devices is still occupied with thetransport and the stacking of a preceding sheet.

The sheet conveyance device, which is known from the state of the art,which was cited above, presents two diametrically opposite slits for thereception of sheet front edges, so that the sheet conveyance device inprinciple is already again prepared to receive a next sheet, while itdeposits a preceding sheet. However, in reality this occurs only if thesheets to be taken over have a fitting format. Indeed, a sheet ispreferentially transferred by transport rollers at the end of atransport path for printing materials to the sheet conveyance device. Agood stacking of the sheet is achieved, in particular, if the transportrollers at that time are just transferring the back edge of the sheet,as soon as the sheet front edge reaches a stop at an output place,because the sheet is then stacked flexibly onto the stack of sheets.This means that the sheet should have a length, which is such that itjust surrounds approximately half of the sheet conveyance device, andthus corresponds approximately to half the circumference of the surfaceof the sheet conveyance device. However, this is far from being alwaysthe case. Longer or shorter formats are also transported. Moreover, itis possible, for example, that heavier and stiffer printing materialcannot be bent to a significant degree without suffering damage, so thatthe radius of the sheet conveyor device, in view of the use of such aprinting material, is chosen to be larger, as a preventive measure, thanwould perhaps be appropriate for the length of the sheet format. On theother hand, to fully use the installation, the sheets should betransported in, as regular as possible a flow, and the gap between twosuccessive sheets should not be too large. However, successive sheetsalso should not overlap.

Thus, it can happen that the free slit, which is intended for the nextreception, could be ready either too early or too late, depending on thesituation. In view of the described situation, it would also not be asolution of the problem to fit the sheet conveyance device with a largernumber of slits (or with other jaw-like openings).

However, the solution according to the invention very definitelypresents optimization possibilities, because an additional sheetconveyance device can be readied, independently and with precise timing,with adaptation to the format of the sheet.

An additional special embodiment of the invention provides for the useof a sheet deflection device which works in cooperation with the sheetconveyance devices, where the sheet deflection device forms, with asurface which serves as support for the sheet, a substantially curvedpath for the sheet to be conveyed, and each sheet conveyance devicespresents at least one overlapping element for overlapping the receivedsheet front edge, in such a manner that the sheet front edge can begrabbed, in a manner so it can be moved along, between one of theseoverlapping elements of a sheet conveyance device and the surface of thesheet deflection device.

If a reception slit for the sheet front edge is used, there is a riskthat the sheet front edge will be damaged in the slit and it may occurthat the sheet is not held sufficiently reliably and in the correctposition until the desired stacking in the slit, into which it only hasbeen inserted.

The invention is therefore based on the secondary problem of indicatinga functional alternative. It is advantageous, in the mentioned solutionaccording to the invention of these problems, to distribute functionsover different elements, for the purpose of achieving a more targeted,and more reliable functionality.

The sheet deflection device substantially assumes the function of a diskbody and it provides a device and a support for the sheet, where thissheet deflection device also does not necessarily have to be in theshape of a disk, rather, according to an embodiment, it can also besegmented in the shape of a wheel or in any other manner.

The sheet conveyance device takes over above all a part of the holdingfunction, by readying an overlapping element, which clamps the sheetfront edge between itself and the surface of the adjacent sheetoverlapping element, and holds it reliably as a result, without damagingthe front edge. These sheet conveyance devices, however, even more mustnot be in the shape of a disk; rather it is preferred that, according toan embodiment of the invention, they are characterized by anarrangement, which substantially includes two armed pivoting beams,which each present, in the area of each one of their two radiallyoutward free ends, an overlapping element. By the overlapping elementsat both ends, each sheet conveyance device is already prepared to takeup a next sheet, while it is depositing a preceding sheet, or at leastshortly thereafter. Thus, the sheet deflection device, which is alreadypreferably substantially symmetrical with respect to an axle ofrotation, is in any case in principle ready in any rotational positionand at all times.

The overlapping element is preferably a tongue or lash with a surface,and also optionally with spring mounted yield, so that an additionalmechanism to prevent damaging the sheet front edge is provided. Here theoverlapping element is substantially a tongue or cover plate, which isapproximately parallel to the curvature path of the sheet deflectionelement.

The next embodiment of the invention provides for the multitude of sheetconveyance devices and the sheet deflection device to be each doubledand arranged on the common axle with mirror symmetry with respect toeach other, in such a manner that all sheet conveyance devices arearranged between the two sheet deflection devices, so that a front sheetedge, in its orientation parallel to the common axle of the sheetconveyance devices and the sheet deflection devices, can be jointlygrabbed by two of the sheet conveyance devices, of which there is atotal of at least four, and the two sheet deflection devices.

In this manner, the sheet is advantageously reliably grabbed over itsentire width and, in particular, a transverse position or rotation dueto the transport is also prevented.

For a particularly reliable grabbing, it is preferred to provide for theside of the overlapping elements of the sheet conveyor devices, which isturned toward the sheet, to be at a smaller radial distance from thecommon axle than the overlapped external side of the sheet which appliesits thickness on the radius of the surfaces of the sheet deflectiondevices, so that the sheet front edge in its travel is forced and bentthrough, in a manner generating tension, in the area of the overlappingelements, approximately in the direction of the common axle.

As is already known from the state of the art, the device according tothe invention as well has a stop for the sheet front edges, with whichthe sheet conveyance devices work in cooperation during the stacking ofthe sheets.

In view of, in particular, sheet formats which are as short as possible,this device according to the invention is preferably characterized by atleast one guiding element which blocks a grabbed sheet at least in thecentrifugal direction, between a grabbing place and a delivery place ofthe sheet to force the sheet to maintain the radius of curvature. Inthis manner, the grabbed and transported sheet is still reliablystacked, in an immediate position, to the surface of the first sheetconveyance device, even if its back edge were released too soon fromtransport rollers.

A particular result of the use according to the invention of at leasttwo sheet conveyance devices is that there time is saved during thestacking of the sheet, if one provides, if desired, at least oneshifting device which is coupled with at least one of the sheetconveyance devices, for a transverse shifting of a sheet to be stacked,in a direction which is substantially parallel to the common axle of thesheet conveyance devices.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment example of a device according to the invention, from whichother inventive characteristics can also be seen, but to which theinvention is not limited in its scope, is schematically represented inthe drawing, in particular to illustrate the operational course of sucha device. In the drawings:

FIG. 1 shows sheet conveyance devices according to the invention in aside view in a first rotational position;

FIGS. 2 through 4 show the sheet conveyance devices in additionalrotational positions; and

FIG. 5 is a perspective view of a device according to the invention withsheet conveyance devices according to FIGS. 1 through 4.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 4 show sheet conveyance devices according to theinvention in a side view in different rotational positions to illustratethe functional course of such an example of a device according to theinvention. FIG. 1 is a representation of a side view of a substantiallydisk shaped sheet deflection device 1, on which a sheet to betransported is placed, which sheet is transferred by the last transportrollers 2, which form the end of the transport path for printingmaterial, to the sheet deflection device 1.

For the forced placement of the sheet on the sheet deflection device,the pin roller 3 is used as a guiding element which blocks in thecentrifugal direction, and which is preferably adjustable along thecircumference of the sheet deflection device 1, in order to be able toguide different sheet formats reliably and for a sufficiently long time.

The device according to the invention includes, in the representation ofFIGS. 1 through 4, additionally two sheet conveyance devices 4, 5, whichare substantially two-armed pivoting beams, and which present, at eachone of their free ends, a cover plate-shaped overlapping element 6. Asheet to be transported can be inserted with its sheet front edge intothe slit between the sheet deflection device 1 and an overlappingelement 6, and held therein, and it can be conveyed by the simultaneousrotation of the sheet deflection device 1 and of the sheet conveyancedevice 4 or 5, each affected by its corresponding overlapping element 6,to a stop 7, and stacked there on a stack of sheets, 8. The two sheetconveyance devices 4, 5 can in principle be rotated independently ofeach other about the common rotation axle 9, so that they can assume thecorresponding different rotational positions in order to take over, inas rapid as possible a sequence, one sheet after the other from thetransport rollers 2, and to be able to deposit them on the stack ofsheets, 8. Each respective position of the determining overlappingelements 6 is better identified in FIGS. 1 through 4 because thepositions are labeled A, B, C, and D to allow them to be distinguished.

With reference to FIGS. 1 through 4, the course of the operation of thedevice according to the invention can thus be described as follows:

The first sheet conveyance device 4 is positioned in such a manner thatthe overlapping element A is in the sheet receiving position. The secondsheet conveyance organ 5 follows the sheet conveyance device 4 with itsoverlapping element D at a short interval.

This is a result of the fact that the overlapping element C is placed insuch a manner on the opposite side (area stop 7) of the second sheetconveyance device 7, that precisely one sheet can be stacked on the stop7.

The second sheet conveyance device 7 can now remain in the describedposition until the first sheet conveyance device 4 with the next sheetto be stacked runs downward and must enter into the area of the stop 7.

This intermediate stop of the overlapping elements 6 in the area of thestop 7, which tends to deposit a sheet on the stop 7, is advantageousif, as preferably provided for, before the stop 7 an offset shift of thesheets is to be carried out, that is if at least one shifting device,which is not shown in further detail, and which is coupled with at leastone of the sheet conveyance devices 1, 4, 5, is provided, for thetransverse shift of a sheet to be stacked in a direction which issubstantially parallel to the common axle 9 of the sheet conveyancedevices.

If the overlapping element A with the next sheet to be stacked has moveddownward and assumed practically the position of the overlapping elementC, then the overlapping element D has already moved into the sheetreceiving position.

Indeed, it is as if the two sheet conveyance devices 4, 5 were chasingeach other, without ever colliding.

As an alternative, the sheet conveyance devices 4, 5 can take over theguidance roller function here.

In this solution it is also important that, after the start of thetransport of a sheet in the direction of the stop 7, the following sheetconveyance device 4, 5 can be moved with an overlapping element 6 underthe sheet to be stacked into the sheet receiving position.

Thus, the small gap between two sheets, which arrive at the transportrollers 2, does not have to be used to lead the next overlapping element6 into the sheet receiving position.

This results in the following sequence of steps:

-   First step/Fourth step (FIG. 1):    -   Sheet conveyance device 4 with overlapping element A is in the        sheet receiving position;    -   sheet conveyance device 5 follows with a short separation after        the sheet conveyance device 4 with the overlapping element D;    -   simultaneously, the sheet conveyance device 5 with the segment C        could deposit a sheet on the stack edge, or cause an offset        movement to be performed there.-   Second step (FIG. 2):    -   Sheet conveyance device 4 moves with the newly received sheet in        the direction of the stop 7;    -   sheet conveyance device 5 still remains in the preceding        position;    -   back-up roller 3 has taken over the sheet transport.-   Third step (FIG. 3):    -   Sheet conveyance device 4 has moved the sheet over the        overlapping element A further in the direction of the stop 7;        sheet conveyance device 5 has turned until the overlapping        element D is in the sheet receiving position.-   Fourth step/First step (FIG. 4):    -   Sheet conveyance device 4 has led the sheet over the overlapping        element A on the stop 7, where it is temporarily stopped. Offset        shift could now be carried out with the sheet located on the        stop 7;    -   the overlapping element D which is in the sheet receiving        position can receive the next sheet.

The sequence of the steps 3 and 4, which has been shown in successiverepresentations, can also take place with temporal overlap. This ispreferably the case if the sheet formats are shorter. While one sheet isstill being conveyed in the direction of the stop 7, the next sheet canalready be inserted in a following overlapping element 6. As soon as thesheet back edge is conveyed out of the intervention area of the back-uproller 3, the next overlapping element 6 with the next sheet can moveinto this back-up roller area.

In fact, the second sheet follows the first one with the correspondinggap. For there to be no gap in the transport area of the overlappingelement 7, after the reception of two very short sheets (in the case ofa total of only four overlapping elements 6, both sheets would be on onehalf of the disk shaped sheet deflection device 1), both sheetconveyance devices 4, 5 are fitted with two overlapping elements 6 andnot with only one. As a result, the gap is always automatically closedagain, without the need to move one overlapping element 6 over half thecircumference of the deflection, in an accelerated manner, into thesheet receiving position.

FIG. 5 is a perspective view of an embodiment example of a deviceaccording to the invention. The same construction elements areidentified with the same reference numerals as in FIGS. 1 through 4.

In FIG. 5 one can see, in particular, that two sheet deflection devices1 and four sheet conveyance devices 4, 5 are arranged on the axle 9 in amirror symmetric arrangement with respect to each other, in such amanner that the two sheet deflection devices 1 are located on theoutside and the sheet conveyance devices 4, 5 are located in between.

1. Device for stacking sheets for a printing machine, including at leasta sheet deflection device (1), which can be driven in rotation, andwhich is provided for receiving a front edge of a sheet and for stackingthe sheet after it has moved through a rotation path, said sheetstacking device comprising: at least two sheet conveyance devices (4, 5)that can be rotated substantially independently of each other about thecommon axle (9), and thus one of said at least two sheet conveyancedevices (4, 5) is ready to receive or grab a next sheet, when anotherone of said sheet conveyance devices (4, 5) is still occupied with thetransport and the stacking of a preceding sheet.
 2. Device according toclaim 1, wherein said sheet deflection device (1), which works incooperation with said at least two sheet conveyance devices (4, 5),forms, with a surface which serves as support for the sheet, asubstantially curved path for the sheet to be conveyed, and each of saidat least two sheet conveyance devices (4, 5) presents at least oneoverlapping element (6) which overlaps the received sheet front edge, insuch a manner that the sheet front edge can be grabbed so it can bemoved along between one of these overlapping elements (6) of a sheetconveyance device (4, 5) and the surface of said sheet deflection device(1).
 3. Device according to claim 2, wherein sheet deflection device (1)is substantially a disk or wheel.
 4. Device according to claim 2,wherein each sheet conveyance device (4, 5) is substantially a two-armpivoting beam which presents, in the area of each of its two radiallyoutward directed free ends, an overlapping element (6).
 5. Deviceaccording to claim 4, wherein said overlapping element (6) is a tongueor cover plate which substantially parallels the curved path of saidsheet deflection element (1).
 6. Device according to claim 5, whereinsaid sheet conveyance devices (4, 5) and said sheet deflection device(1) are in each case doubled, and arranged, on the common axle (9), inan arrangement with mirror symmetry to each other, in such a manner thatall sheet conveyance devices (4, 5) are arranged between the two sheetdeflection devices (1), so that a sheet front edge, in its orientationparallel to the common axle (9) of said sheet conveyance devices (4, 5)and said sheet deflection device (1), can be grabbed jointly by two ofsaid sheet conveyance devices (4, 5), of which there is a total of atleast four, and said two sheet deflection devices (1).
 7. Deviceaccording to claim 6, wherein the side of the overlapping elements (6)of the sheet conveyance devices (4, 5), which is turned toward thesheet, is at a smaller radial distance from the common axle (9) than theoverlapped external side of the sheet which applies its thickness ontothe radius of the surface of said sheet deflection devices (1), so thatthe sheet front edges, in their travel, are forced and bent through, ina tension producing manner, in the area of said overlapping element (6)approximately in the direction of the common axle (9).
 8. Deviceaccording to claim 2, wherein a stop (7) for the sheet front edges, withwhich the sheet conveyance devices (4, 5) work in cooperation during thestacking of the sheets.
 9. Device according to claim 2, wherein at leastone guiding element (3), which blocks a grabbed sheet at least in thecentrifugal direction, between a grabbing place and a delivery place ofthe sheet to force the sheet, to maintain the radius of curvature. 10.Device according to claim 1, wherein at least one shifting device whichis coupled to at least one of said sheet conveyance devices (4, 5) orsaid sheet deflection device (1), to transversely shift a sheet to bestacked, where the shift is oriented substantially parallel to thecommon axle (9) of said sheet conveyance devices.